Middle-aged people who smoke, are diabetic or have high blood pressure are far more likely to suffer from dementia, research reveals today.

Smokers aged between 46 and 70 have a 70% higher risk of developing chronic memory loss, according to a study reported in Britain's Journal of Neurology, Neurosurgery and Psychiatry. The chance of people with diabetes getting dementia is more than doubled because of their condition, while in those with raised blood pressure it is increased by 60% compared with people without that problem.

A separate study today shows that people may be able to ward off the onset of dementia by stimulating their brain regularly through everyday activities such as reading, writing and playing card games. That research, in the American journal Neurology, offers further evidence that mental exercise can help delay cognitive impairment.

Dr Susanne Sorensen, head of research at the Alzheimer's Society, said: "Interestingly this research has found that memory loss in people who are in the very early stages of the condition may be delayed by ordinary activities that engage the brain, whether they were well-educated in early life or not.

"This research suggests that exercising your brain as well as your body may play a role in the fight against dementia."

The results in the British journal show that middle-aged people should immediately quit smoking and make lifestyle changes that will help control the two medical conditions, rather than waiting until they are pensioners, to reduce their risk of succumbing to the incurable brain-wasting disease.

Previous studies have pinpointed those three causes as significant risk factors, but the American research has calculated by how much the risk for someone in any of the three categories rises.

Researchers at four US universities, as well as the Johns Hopkins hospital in Baltimore, studied 11,151 men and women aged between 46 and 70 whose health was assessed in 1990-92 as part of the Atherosclerosis Risk in Communities study, who were then checked in 2004 to see if they had been hospitalised with dementia.

The study said: "Smoking, hypertension and diabetes were associated with a higher risk of the outcome." However, the researchers uncovered no link between either obesity or a high level of blood cholesterol and dementia.

"Our results suggest that, for prevention of dementia, control of cardiovascular risk factors starting in midlife is likely to be more important in the prevention of dementia than control starting later on."

The study, one of the first to include non-whites, also found that African-Americans were two and a half times more likely than whites to require hospital treatment for dementia, and that female African-Americans had the highest rates of all among the 11,151 participants, of whom 23% were African-American.

Neil Hunt, chief executive of the Alzheimer's Society, said: "Dementia is one of people's biggest fears in later life but very few people realise that there are things they can do to reduce their risk of developing this devastating condition.

"This study [in the British journal] adds weight to the growing evidence that a healthy heart means a healthy brain."

People should keep active, eat a balanced diet, not smoke and have their blood pressure and cholesterol checked regularly, he added.